#include<iostream>

using namespace std;

//全局变量声明
int g;

/*
  全局变量自动初始化值
  int 0
  char '\0'
  float 0
  double 0
  pointer null
*/


int main()
{
    //局部变量声明
    int a,b;

    //实际初始化

    a = 10;
    b = 20;
    g = a + b;

    cout << g;

    return 0;
}